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| United States Patent |
6,177,209
|
|
Okutoh
|
January 23, 2001
|
Battery protector having a positive temperature coefficient element
Abstract
A small protector is provided for a high energy density battery such as a
lithium ion battery. A flat sheet form of leading portion extending from a
positive temperature coefficient element is provided thereon with at least
one battery protecting circuit element for detecting at least one
abnormality selected from overcharging, over-discharging, overcurrent, and
unusual temperature to cut off a current passing therethrough. A fail-safe
mechanism is achieved for the actuation of the positive temperature
coefficient element and the actuation of the battery protecting circuit
element.
| Inventors:
|
Okutoh; Tadashi (Kawasaki, JP)
|
| Assignee:
|
Nippon Moli Energy Corp. (Yokohama, JP)
|
| Appl. No.:
|
126425 |
| Filed:
|
July 30, 1998 |
Foreign Application Priority Data
| Current U.S. Class: |
429/62; 429/7; 429/92 |
| Intern'l Class: |
H01M 002/00; H01M 010/50; H01M 010/48 |
| Field of Search: |
429/61,62,91,7,92
|
References Cited
U.S. Patent Documents
| 5609972 | Mar., 1997 | Kaschmitter et al. | 429/56.
|
| 5631100 | May., 1997 | Yoshino et al. | 429/62.
|
| 5689173 | Nov., 1997 | Oosaki et al. | 320/35.
|
| 5939217 | Aug., 1999 | Tamura et al. | 429/7.
|
Primary Examiner: Kalafut; Stephen
Assistant Examiner: Dove; Tracy
Attorney, Agent or Firm: Armstrong, Westerman, Hattori, McLeland & Naughton
Claims
What we claim is:
1. A battery protector comprising:
a positive temperature coefficient element;
a flat sheet form of leading portion extending from said positive
temperature coefficient element;
at least one battery protecting circuit element provided on said flat sheet
form of leading portion, electrically connected in series with said
positive temperature coefficient element, for cutting off a current
passing therethrough detecting at least one abnormality of overcharging,
over-discharging, overcurrent, and unusual temperature.
2. The battery protector according to claim 1, wherein said battery
protecting circuit element is mounted on said flat sheet form of leading
portion extending from said positive temperature coefficient element while
said battery protecting circuit element is provided on a circuit
substrate.
3. The battery protector according to claim 1, wherein said battery
protecting circuit element and said flat sheet form of leading portion
extending from said positive temperature coefficient element are thermally
coupled together via a heat radiating sheet.
4. The battery protector according to claim 2, wherein said battery
protecting circuit element and said flat sheet form of leading portion
extending from said positive temperature coefficient element are thermally
coupled together via a heat radiating sheet.
5. The battery protector according to claim 1, wherein said unusual
temperature is sensed by a temperature sensor element located in the
vicinity of said positive temperature coefficient element, or found from a
voltage drop across said positive temperature coefficient element.
6. The battery protector according to claim 2, wherein said unusual
temperature is sensed by a temperature sensor element located in the
vicinity of said positive temperature coefficient element, or found from a
voltage drop across said positive temperature coefficient element.
7. The battery protector according to claim 3, wherein said unusual
temperature is sensed by a temperature sensor element located in the
vicinity of said positive temperature coefficient element, or found from a
voltage drop across said positive temperature coefficient element.
8. The battery protector according to claim 4, wherein said unusual
temperature is sensed by a temperature sensor element located in the
vicinity of said positive temperature coefficient element, or found from a
voltage drop across said positive temperature coefficient element.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to a protector for secondary
batteries, and particularly to a protector for a specific secondary
battery of high energy density, e.g., a lithium ion battery using a
lithium ion doping or de-doping material as an active negative electrode
material. More particularly, the present invention is directed to a
battery protector of small size.
A lithium ion battery using a lithium ion doping or de-doping carbonaceous
material can output high voltage and has high energy density albeit being
light in weight, and so is now widely used on portable equipment. Although
secondary batteries may be used over and over by charging, yet their
performance may become worse upon charging. Especially in the case of a
lithium ion battery, an overcharge preventing protector is incorporated
therein so as to prevent overcharging which may otherwise cause
precipitation of metallic lithium or an electrolyte leakage due to the
actuation of a pressure valve due to gas generation upon overcharging,
resulting in thermal runaway, and fuming. In addition, an over-discharge
protector, a current limiter, a device for preventing a battery
temperature increase during charging and discharging are provided.
Equipment using batteries as a power source may operate with batteries
having different capacities and a different number of batteries depending
on what purpose it is used for. Used for this reason is a battery pack
which is attachable to or detachable from equipment and contains one or
more batteries.
A battery protector should be regulated for each battery capacity, and so
is built in the battery pack. This is also true of a positive temperature
coefficient element (PTC) that can be actuated by heat generated by an
overcurrent due to short-circuiting or a battery temperature increase to
cut off a current passing therethrough, because it should be located in
the vicinity of a battery.
Small yet large-capacity batteries are required for size reductions of
equipment using batteries as a power source. However, a battery protector
is built in an individual battery pack. This, combined with the size
limitation of the battery pack, is one factor of a reduction in the amount
of active battery materials.
The present invention is directed to a protector for a secondary battery
having high energy density such as a lithium ion battery using a lithium
ion doping or de-doping carbonaceous material as an active negative
electrode material. A particular object of the invention is to provide a
battery protector of small size.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(A) and 1(B) are illustrative of one embodiment of the battery
protector having a positive temperature coefficient element according to
the invention.
SUMMARY OF THE INVENTION
The present invention provides a battery protector having a positive
temperature coefficient element, wherein:
a flat sheet form of leading portion extending from said positive
temperature coefficient element is provided thereon with at least one
battery protecting circuit element for detecting at least one abnormality
selected from overcharging, over-discharging, overcurrent, and unusual
temperature to cut off a current passing therethrough.
Preferably, the battery protecting circuit element is mounted on the flat
sheet form of leading portion extending from the positive temperature
coefficient element while the battery protecting circuit element is
provided on a circuit substrate.
Preferably, the battery protecting circuit element and the flat sheet form
of leading portion extending from the positive temperature coefficient
element are thermally coupled together via a heat radiating sheet.
Preferably, the unusual temperature is sensed by a temperature sensor
element located in the vicinity of the positive temperature coefficient
element, or found from a voltage drop across the positive temperature
coefficient element.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the battery protector having a positive temperature coefficient element
according to the invention, the positive temperature coefficient element
is integral with a substrate comprising a battery protecting circuit for
protecting a battery against overcharging, over-discharging,
over-currents, temperature increases, etc.
In a positive temperature coefficient element, generally, a leading portion
thereof is formed of a conductor having a large area, such as a nickel
sheet, so as to prevent a voltage drop due to a current passing
therethrough. In the present invention, a flat sheet form of leading
portion is designed to extend from the positive temperature coefficient
element.
The present invention is now explained with reference to FIGS. 1(A) and
1(B).
FIGS. 1(A) and 1(B) are a plan view and a sectional view of one embodiment
of the battery protector having a positive temperature coefficient element
according to the invention, respectively.
A battery protector 1 comprises a positive temperature coefficient element
2 from which leading portions 3 and 4, each in a flat plate form, extend.
The leading portion 4 is provided with a circuit substrate 6 having a
battery protecting circuit element 5, and makes an electrical connection
with the circuit substrate 6. The circuit substrate 6 is provided with a
terminal 7 for connection to a battery (batteries) and equipment, and a
ground terminal 8. The circuit substrate 6 also comprises a heat radiating
sheet 9 for thermally coupling the battery protecting circuit element 5 to
the leading portion, as shown by a broken line in FIG. 1(A). A temperature
sensor element 10 is located in the vicinity of the positive temperature
coefficient element 2.
With the battery protector 1 positioned in place, either one of the leading
portion 3 and the connecting terminal 7 of the circuit substrate 6 is
connected to a positive-side terminal of the battery, and the ground
terminal 8 is connected to a ground-side wiring. The positive temperature
coefficient element 2 is positioned in the vicinity of the battery so
that, when the battery generates heat, the heat can be well transmitted
thereto.
When the battery is in normal operation, heat generated by a current in the
battery protecting circuit element 5 is radiated from the heat radiating
sheet 9 and the leading portion thermally coupled thereto.
When an excessive current passes through the battery by reason of
short-circuiting, etc., the positive temperature coefficient element 2
generates heat and increases in resistance, so that the current passing
therethrough can be controlled. It is preferable to sense the temperature
of the positive temperature coefficient element 2 by means of the
temperature sensor element 10. When the temperature of the element 2 is
found to exceed a preset temperature, a current cutoff circuit in the
battery protecting circuit element is actuated to cut off the current
passing therethrough.
Instead of sensing the temperature increase of the positive temperature
coefficient element by the temperature sensor element, it is also
acceptable to find the temperature inherent in the positive temperature
coefficient element from the voltage across the positive temperature
coefficient element and the magnitude of the current passing therethrough.
If the found temperature exceeds a preset temperature, the current cutoff
circuit in the battery protecting circuit element 5 is then actuated.
Thus, the battery protector of the invention has a fail-safe mechanism for
cutting off the current in response to an increase in the resistance of
the positive temperature coefficient element, and for cutting off the
current by the actuation of the current cutoff circuit in the battery
protecting circuit element. Consequently, it is possible to protect the
battery with great reliability.
With the present invention where the positive temperature coefficient
element increasing in electrical resistance due to the generation of heat
by an excessive current is integral with the battery protecting circuit
element, it is possible to reduce the size of a battery pack and, hence,
increase capacity per volume of the battery pack.
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